May 2012 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

RE: [RFC]confusions about 'struct' define
by Rajat Sharma May 30, 2012

May 30, 2012

This might be the case of cyclic dependency where header files defining these structures are also including this .h file. -Rajat From: harryxiyou Sent: 30-05-2012 23:08 To: Gaurav Jain Cc: Greg-Kroah-Hartman; Harry Wei; kernelnewbies(a)kernelnewbies.org Subject: Re: [RFC]confusions about 'struct' define On Thu, May 31, 2012 at 1:20 AM, Gaurav Jain <gjainroorkee(a)gmail.com> wrote: Hi Gaurav, > Those are forward declarations as they are being used in defining struct > bus_attribute. It's nothing special about GNU-C. That's the case for ANSI-C > too. Pretty standard. > Hmmm.., that is to say, they may be used before definitions in this file or defined in other files like 'struct iommu_ops;' field (Actually, i can not find this field's definition in this file). However, if it has been defined in other header files, we need not declare here, right? -- Thanks Harry Wei _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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cache policy of arm mmu
by Jacky lin May 29, 2012

May 29, 2012

Hi all, I found that the cache policy in after ARMv6 is always set as writeback mode in mmu.c. static int __init early_cachepolicy(char *p) { ... if (cpu_architecture() >= CPU_ARCH_ARMv6) { printk(KERN_WARNING "Only cachepolicy=writeback supported on ARMv6 and later\n"); cachepolicy = CPOLICY_WRITEBACK; } ... } Does anyone know why and provide some documents or links for that? Thanks so much! Cheers, Jacky

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Incremental Linking
by somanath sahoo May 28, 2012

May 28, 2012

Hi, As newbie in linux kernel, I would like to understand the concept of "incremental linking " w.r.t to linux kernel module. I have read that kernel loadable modules are being generated and inserted into a running kernel due to this "incremental linking " technology. If anyone can provide me some pointers to understand the "incremental linking" concept, it will be needful. Thanks, Somanath

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Encfs detailed design guide?!! [hope this is relevant to this forum]
by SaNtosh kuLkarni May 27, 2012

May 27, 2012

Any help regarding Encfs (encrypted file system) detailed design. Any suitable link would be helpful.Thanks. -- *Regards, Santosh*

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creation, context switch time of process and thread
by Srinivas Ramanan May 27, 2012

May 27, 2012

Can someone give the information of following typical values in Kernel 3.x in a 2Ghz machine with sufficient RAM Process creation time ? Process context switch time ? pthread creation time ? pthread context swich time ? kernel thread creation time ? kernel thread context swich time ? What is the best way to measure these values? I wrote a simple test for measuring kernel thread context switch A simple test like 1. get_time(start) 2. schedule(); 3. get_time(end) 4. print( context sw time = (end-start) ) But it doesnt seem to work correctly. Thanks. Ramanan

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how to study process schedule
by 王哲 May 26, 2012

May 26, 2012

Hello Everyone I want to study process schedule.but i don't kown how to begin. and i like to write some kernel modules to learn more about kernel. if i want to write some modules about schedule.what i can write. Thanks a lot for your help! wanny -- ---------------------------------------------------------------------------------------------- WangZhe Xi'an Shanxi CHINA qq 785924174 blog blog.163.com/zhe_wang_2009 ----------------------------------------------------------------------------------------------

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anyone know what a "lockless ioctl" is?
by Robert P. J. Day May 25, 2012

May 25, 2012

reading a course outline and there's a reference to "lockless ioctls". no idea what that is, and google doesn't make it any clearer: http://www.google.ca/#hl=en&sclient=psy-ab&q=%22lockless+ioctl%22&oq=%22loc… did such a thing ever exist? rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Fwd: [Q] USB urb completion handler
by Ezequiel Garcia May 24, 2012

May 24, 2012

On Mon, May 7, 2012 at 2:48 PM, Peter Senna Tschudin <peter.senna(a)gmail.com> wrote: > http://www.makelinux.net/ldd3/chp-13-sect-3#chp-13-sect-3.4 > > " If the function succeeds, the completion handler of the urb (as > specified by the complete function pointer) is called exactly once > when the urb is completed. When this function is called, the USB core > is finished with the URB, and control of it is now returned to the > device driver." > Bingo! Because the driver will only submit *one* urb at a time, how could it possible have more than one completion handlers called at a time? I wasn't thinking with the right half of my brain. Thanks, Ezequiel.

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Communication between kernel and kernel module
by drewd77.gm May 23, 2012

May 23, 2012

Hi, Is there any way to call a function defined in a kernel module from within the kernel proper? Here's what I'm trying to do: I'm trying to keep track of when and for how long a process is being executed on the processor, i.e. I need to know when context switches occur. There is a function called context_switch() in linux/kernel/sched/core.c that is called whenever a context switch happens. I would like to call a function in a kernel module I've written from within context_switch() and pass some data to it. I've seen how to communicate between user space and kernel space, such as using a file in /dev or using system calls, but not how to communicate within the kernel itself. Regards, Drew

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A question about fs
by 王哲 May 23, 2012

May 23, 2012

Hello Everyone: The first time to study fs ,and write a simple module to traverse the double list with super_block. and the output of module is different with the result from the command cat /proc/filesystems. the output fs of module is 23,and the output fs of cat /proc/filesystems is 26. why? My Environments: # uname -r 2.6.39.1 # lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 11.04 Release: 11.04 Codename: natty gcc version 4.5.2 (Ubuntu/Linaro 4.5.2-8ubuntu4) my code is as followed: #include<linux/module.h> #include<linux/init.h> #include<linux/sched.h> #include <linux/fs.h> #include <linux/list.h> #include <linux/spinlock.h> #define addr_super_blocks 0xc173d0a0 #define addr_sb_lock 0xc18f3ba0 #ifndef offsetof #define offsetof(type, field) ((long) &((type *)0)->field) #endif /* offsetof */ #ifndef container_of #define container_of(ptr, type, member) ({ \ const typeof( ((type *)0)->member ) *__mptr = (ptr); \ (type *)( (char *)__mptr - offsetof(type,member) );}) #endif static __init int sbinfo_init(void) { struct list_head *p; int count = 0; struct super_block *sb; spin_lock((spinlock_t *)addr_sb_lock); p = (struct list_head *)addr_super_blocks; p = p->next; for (;p != (struct list_head *)addr_super_blocks;p = p->next) { sb = container_of(p,struct super_block,s_list); printk("<0>filesystem name:%s\n",sb->s_type->name); count++; } spin_unlock((spinlock_t *)addr_sb_lock); printk("<0>----------------->%d\n",count); return 0; } static __exit void sbinfo_exit(void) { printk("<0> bye! \n"); } module_init(sbinfo_init); module_exit(sbinfo_exit); MODULE_LICENSE("GPL"); and output: [ 4196.218726] filesystem name:sysfs [ 4196.218732] filesystem name:rootfs [ 4196.218735] filesystem name:bdev [ 4196.218737] filesystem name:proc [ 4196.218740] filesystem name:tmpfs [ 4196.218742] filesystem name:devtmpfs [ 4196.218745] filesystem name:debugfs [ 4196.218747] filesystem name:sockfs [ 4196.218750] filesystem name:pipefs [ 4196.218752] filesystem name:anon_inodefs [ 4196.218755] filesystem name:securityfs [ 4196.218757] filesystem name:devpts [ 4196.218760] filesystem name:hugetlbfs [ 4196.218762] filesystem name:mqueue [ 4196.218765] filesystem name:sysfs [ 4196.218767] filesystem name:fusectl [ 4196.218769] filesystem name:ext4 [ 4196.218771] filesystem name:tmpfs [ 4196.218774] filesystem name:tmpfs [ 4196.218776] filesystem name:tmpfs [ 4196.218778] filesystem name:ext4 [ 4196.218780] filesystem name:fuse [ 4196.218783] filesystem name:binfmt_misc [ 4196.218786] ----------------->23 and cat /proc/filesystems output: nodev sysfs nodev rootfs nodev bdev nodev proc nodev cgroup nodev cpuset nodev tmpfs nodev devtmpfs nodev debugfs nodev securityfs nodev sockfs nodev pipefs nodev anon_inodefs nodev devpts ext3 ext2 ext4 nodev ramfs nodev hugetlbfs nodev ecryptfs nodev fuse fuseblk nodev fusectl nodev pstore nodev mqueue nodev binfmt_misc if anyone knows please help .Thanks -- ---------------------------------------------------------------------------------------------- WangZhe Xi'an Shanxi CHINA qq 785924174 blog blog.163.com/zhe_wang_2009 ----------------------------------------------------------------------------------------------

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